It's all about how to display concepts visually, particularly when it's involving with spatial data. In most cases you will need a map to find out locations, positioning, and understand some phenomenon or pattern occurring in an area. 1. Create a thematic map from scratch for your custom needs 2. Edit an existing map 3. Register an image with known coordinate, so I can create a rectified image 4. Customize online map such as Google Earth 5. Create a topographic contour or 3D topography models 6. Even a more complex map making and GIS purpose (demographic data, etc)